Pumpkin pie filling contains spices like allspice and nutmeg plus added sugar. Canned pumpkin is just canned pumpkin. You can sub canned pumpkin for pumpkin pie filling if you add spices, but it's not a good idea to do the reverse!

Pumpkin pie filling is already spiced and I think it may be sweetened also, someone correct me if I am wrong, Pumpkin puree is just pumpkin no sweeteners or spices. You can use either or but the puree will have to be spiced and sweetened,

Just checked a can of pumpkin puree and it has one ingredient listed: pumpkin.
Perhaps you are getting ready to make those divine salted pumpkin caramels? They are on my list as soon as the weather cooperates.

Straight canned pumpkin - as opposed to pumpkin pie filling - is good for dogs when they have stomach troubles. Our vet has recommended this when we have called to ask what to do with our dogs who are having a "bad stomach" (aka, the runs). Sorry - unpleasant - but good to keep on hand (along with brown rice) if you are a dog owner. :)